1. Field of the Invention
The present invention relates to a dilatation balloon assembly utilized for the implantation of an endoprosthesis device, such as a stent, within a vessel such as a blood vessel in a living body.
2. Description of the Prior Art
Recently endoprosthesis devices, such as stents, have come into more common use in treating stenosis strictures or aneurysms in a blood vessel. Such a device or stent is implanted within a vascular system to reinforce a collapsing, partially occluded or abnormally dilatated section of the blood vessel or to effect and reestablish a connection between blocked vessels.
A common procedure for implanting a stent is to first open the region of the vessel with a dilatation balloon catheter. Then, a stent is positioned in the opened area in a position to bridge the opened area, which may be a weakened portion of a blood vessel or an opened area of reconnection between blood vessels.
In the field of angioplasty where a dilatation balloon catheter is placed in a constricted stenotic region and then inflated to expand and open that region, it has been found that the dilatating or opening of the restricted stenotic region, while initially relieving the problem of an occluded restricted passageway in the vessel, does not provide a sufficiently long term solution to the problem. In this respect, after a relatively short period of time of a few years the vessel often returns to its original occluded state, i.e., postangioplasty restenosis, as a result of the blood vessel collapsing inwardly or as a result of the rebuilding of plaque in the stenotic region.
What has proved to be more successful is the implantation of a stent after the restricted stenotic region has been dilatated. Recent studies indicate that by use of a stent the constriction of the blood vessel in the region of stenotic restriction is maintained open for a much longer period of time than with dilatation alone. Articles describing the procedures used and the results obtained are set forth below:
"Expandable Intrahepatic Portacaval Shunt Stents", Palmaz et al "AJR: 145", pp. 821-825. October 1985 PA1 "Expandable Intraluminal Graft: A Preliminary Study", Palmaz et al, Vol. 156, No. 1, pp. 73-77, "Radiology", July 1985 PA1 "The Palmaz Stent: A Possible Technique for Prevention of Postangioplasty Restenosis", Levin, Volume 169, pp. 87374, "Radiology" September 1988 PA1 "Intraluminal Stents in Atherosclerotic Iliac Artery Stenosis: Preliminary Report of a Multicenter Study", Palmaz et al, Volume 168, pp. 727-731, "Radiology", September 1988
As a result, there is an increasing use of stents and dilatation balloon assemblies for implanting stents.
Examples of prior art stents can be found in the following U.S. patents:
______________________________________ U.S. Pat. No. Patentee ______________________________________ 4,140,126 Chaudhury 4,503,569 Dotter 4,733,665 Palmaz 4,776,337 Palmaz 4,795,458 Regan 4,880,882 Gianturco ______________________________________
Examples of typical prior art dilatation balloon catheter assemblies can be found in the Gruntzig et al. U.S. Pat. No. 4,195,637 and the Simpson et al. U.S. Pat. No. 4,323,071, the disclosures of which are incorporated herein by reference.
A common problem that has been incurred with the use of dilatation balloon assemblies for implantation of and placement of a stent is the inability of the deflated balloon to disengage from the stent after the stent has been expanded. This phenomena is found most frequently in P.E.T. balloons where the balloon, upon collapsing, tends to flatten out under negative pressure producing a flat or "wing-like" configuration which is wider than the inflated diameter of the balloon (.pi.R).
In this respect, a 3.0 mm balloon can produce a 4.7 mm wide plane when it is collapsed.
In addition to the disengagement problem found during the stent implanting or placement, the edges of the wings are "blade-like" and sharp enough to cause serious damage to severely diseased (and even healthy) vessels when the deflated, flattened "wing-like" balloon is withdrawn from a blood vessel in a PTCA procedure.
As will be described in greater detail hereinafter, the present invention provides a balloon design for a dilatation balloon assembly which results in the- balloon having a lateral or cross-sectional extent when it is partially collapsed or fully collapsed, which is less than the diameter of the fully inflated balloon which assumes a generally cylindrical shape. In this way, the creation of a "wing-like" or "blade-like" deflated balloon with sharp edges and with a width or lateral extent greater than the inner diameter of the stent or of the blood vessel through which it is drawn is eliminated, thereby minimizing if not altogether eliminating the possibility of trauma to the blood vessel when the collapsed/deflated balloon is withdrawn from the stent and the vessel.